Just thought I would add this to the conversation... I spent two nights in the hospital due to a lung infection. The docs told me the likely cause was due to my lungs being irritated because of severe coughing spasms. They asked if I smoke cigs, I said yes and that this was probably the cause. Maybe some bad tobacco.
In truth, it started during the 4/20 celebration and having smoked so much under-flushed and/or under-cured weed. Dumb-ass that I am sometimes,

on my last visit I sampled some gear that probably was under-flushed. I had coughing spasms so severe that I coughed up blood, NOT GOOD. A weeks worth of antibiotics later, the infection is gone.
I've noticed that if there's a peculiar chemical scent, it's probably under-flushed gear, esp. when buds are pulled apart.
Nothing happy about bad weed...